Have you tested it on a few other games too? Do you get the same problems. Its interesting how it gradually get worse as the seconds go by, kind of points to some Temp issues or corruption usually.
Thats what i think he described it to look like.
during beta though, I had a similar issue, I fixed it (on win 7) by completely removing catalyst and my display drivers, then letting windows install its own graphics drivers automatically
doing this also made a few other games run smoother, and my card a little more stable
I made a post on a similar thread, as I had the same problem & managed to solve it (same graphics card ATI Radeon M HD 4300)
I downloaded the drivers from the laptop manufacturers site (Dell in my case). They worked perfectly. Just remember to remove the others, then reboot then install the dell-supplied ones.
I also just recently installed the newest cataclyst drivers. Removed them, let Windows 7 install its own driver et voila, no problems at all!
Thank you all!